Sealed feedthroughs for electric conductors have been known for a long time, and applications to optical sensors and optical fiber links are widespread. They require sealed feedthroughs providing passage of the optical signal and an insulation between two media.
Optical sealed feedthroughs available in the industry are based on the use of polymer compounds providing a mechanical link between the optical fiber and the mechanical support. This technology can only be implemented in the factory over a short optical fiber length.
The medium requirements in terms of pressure, nature of the fluids, temperatures, service life limit the use of certain polymer materials. Polymer materials are not inert. Their mechanical properties change with time, age, and they no longer act as sealed barriers.
Another optical fiber sealed feedthrough technology consists in using an optical. fiber locally coated with a metal deposit layer on the glass of the optical fiber. This metal deposit is used as a bonding base for a metal solder providing continuity and cohesion with the metalllic support. This technique requires preparation of the optical fiber and soldering that can only be carried out in the factory over a reduced optical fiber length since the optical fiber has to be slipped into the conduit of the support which is a passage about 0.2 mm in diameter and about 20 mm in length.